On average how many from a UPT drop rotary wing? Are those slots hard to drop/ highly competitive? Need to be top 3 in your UPT class? 

Usually 1 per class.  Maybe.  No way to answer the rest of your questions.  Depends on how many people in your class want helo's.

Just left Vance not too long ago. If you are set on helos, let your flight CC know as soon as possible. Usually it's 1 per class, but I'm in a class now at rucker that has 3 guys from the same upt class from the same T6 base. One of the slots actually came from a guy in my class even though we tracked after them. He traded to a guy that was in the que for toners, so anything's possible. 

It can get competitive if they're unable to get more than 1-2 slots for your class and 4 of you want helos. The class sizes at rucker have increased however. Traditionally it seems that they've put through 6 guys on average, now its looking like 8 will be the norm.

Best of luck.